Homo habilis differs from Australopithecus
at the base of the skull.The foramen
magnum (the opening for the spinal chord) is closer to the middle of the
skull and the skull base is reduced in length but increased in width.The face decreased in width and the nasal opening
was more sharply defined.The postcanine
teeth were smaller than in Australopithecus.

Its cranial capacity was 500 to 800 cc. and
values increase from the earliest specimens to latest ones.This range overlaps with Australopithecus at the low end and Homo erectus at the high end. It can be debated (indeed, there has
been a debate several decades long) on whether early H. habilis should be classified as Australopithecus and late H.
habilis should be called Homo
erectus.H. habilis stood approximately 5 foot tall and weighed 100 pounds
with females being smaller than males (Leakey, 1973b; Wood, 1987; Leakey,
1971b; Hughes, 1977; Johansen, 1987; Bilsburough,
1988; Tobias, 1972).Early Homo populations coexisted with australopithecines
(Johanson, 1976).

In one brain endocast, there is a bulge corresponding
to Broca’s area (an important speech center) in modern human brains.Two aspects of wrist bones (the scaphoid tubercle and the articular
surface of the trapezium) were chimp-like.The thumb was similar to humans in the carpo-metacarpal joint and
the flattened metacarpal surface.The foot was less flexible than in chimps and
its degree of possible abduction was limited.Some characteristics of the lower leg were primitive and others
were advanced, not found in any ape (Susman,
1982; Skelton, 1986).

Homo habilis is translated as “handy man”
referring to the simple stone tools found at many sites (Toth,
1985; Leakey, 1970).Some feel that
the variation in skulls is too great to accommodate in one species and classify
some Homo habilis skulls as Homo rudolfensis (Wood,
1992; Wood, 1999)

.

Although humans are not speedy sprinters compared to quadrupeds and running is metabolically twice as expensive as it is for many other animals, humans are the only primates and one of the few mammals which practices endurance running. (Dogs, hyenas, wildebeest, and horses are also capable of endurance running.) It is thought that endurance running evolved with the genus Homo given that some of the specializations which allow endurance running (such as short toes, an adducted big toe, a more balanced head, neck ligaments, and an enlarged calcaneus) evolved in Homo habilis, other features (such as enlarged semicircular canals, shorter forearms, and larger hip, leg, and back muscle attachment sites, longer legs, and a stronger sacroiliac joint) evolved in Homo erectus, and several other features (a head which was more independent from the shoulder, a narrow pelvis, an arched foot, and a long calcaneal tendon) evolved early in the Homo lineage although the precise point is not known (Bramble, 2004).

Hominids seemingly intermediate between Homo habilis
and Homo erectus traveled outside
Africa 1.6 million years ago.The hominids which first arrived in central
Asia possessed smaller brains, some only
half the size of modern humans and smaller than usual for Homo erectus.They were small-bodied,
similar in size to Homo habilis (Wong, 2003a).

The following image compares a Homo habilis skull to that of a female bonobo chimp.

Homo erectus

DATES:
1.8 million years ago to as late as10 to 27 thousand years ago (have been
dated with K/Ar, Ar/Ar, U series, ESR, and faunal dating methods)

The cranial capacities range from 750 to
1225 cc; early forms average 900 cc; later forms average 1100 cc.The depth and robusticity of the zygomatic bone
differs from modern humans.H. erectus is similar to H. habilis in its protruding jaws, large
molars, lack of a prominent chin, thick brow, and the long, low skull.H. erectus
had human limb proportions and human body shape (it was the first hominid
to have this). Homo erectus increased the length of its thighs and the hips became more human-like (McHenry, 2006). Its skeleton more robust than modern
humans, suggesting considerable strength (Rightmire,
1981; Brown, 1985; Leakey, 1973; Walker, 1981; Day, 1971; Clark, 1976;
Leakey, 1976; Wolpoff, 1984.There was some sexual dimorphism in the skeleton
and one specimen shows signs of hypervitaminosis A (Walker, 1982).

Fossil specimens dating from about 1.75 million years ago discovered at Dmanisi, in the Republic of Georgia have been tentatively identified as the most primitive known Homo erectus/Homo ergaster. Although the most primitive skull whose classification as a member of Homo is not in dispute, it resembles Homo habilis. It appears that early hominids similar to Homo habilis migrated from Africa prior to the evolution of the more typical Homo erectus form (Vekua, 2002).

Homo
erectus is considered to be the first hominid to travel out of Africa (although a find from China and others in Central
Asia may belong to H. habilis rather than H. erectus). Homo erectus
is known from Asia (Java, China, Pakistan, and Georgia) as of 1.7
million years ago and the Middle East as of 1.5 million years ago (Gabunia, 1995; Klein, 1973; Larick,
1996; Howells, 1980)

Homo erectus is known in Java as early as 1.8 million years
ago and as late as 50,000 years ago.The
combination of very thick crania and evidence of healed skull fractures
and head trauma have caused some to propose that male Homo erectus fought
with each other using clubs (Boaz, 2004).The last Homo erectus
populations existed in Java between 27 and 53 thousand years ago dates
which overlap with the existence of Homo
sapiens sapiens in the region (Gibbons, 1996; Thorne, 1972; Swisher,
1996).The earliest African forms of Homo erectus have smaller and more projecting
noses.Some researchers classify
these specimens as Homo ergaster
and feel that Homo ergaster
or some pre-erectus population
migrated from Africa before H. erectus
proper evolved.One find of Homo from 1 million years ago from Afar
(near the Red Sea) is similar to H. ergaster
but also has characteristics of Homo sapiens.Some anthropologists
feel some skeletal characteristics (the frontal keel, torus mandibularis,
os epactale, and incisor shape) of Asian erectus populations indicate that there was interbreeding between
these populations and later H. sapiens
emigrants from Africa.The transitional nature
of the fossil material makes it difficult to assert which populations
should be regarded as separate species. (Dean, 1995;
Lewin, 1989; Wolpoff, 1984; Turner,
1989; Gibbons, 1998; Abatte, 1998).

A skull similar to the Dmanisi skull (considered an early Homo erectus) has been found representing a toothless individual. This suggests that the diet of these hominids included soft food items and perhaps that the social structure of this hominid allowed for support from other members of the group (Lordkipanidze, 2005).

The skeleton of an infant Homo erectus indicates that the endocranial volume was within variations for Homo sapiens and distinct from the chimpanzee range (Leigh, 2006).

Homo fossils are known in the Caucasus since about 1.8 million years ago, Spain and Italy from 800,000 years ago and northern Europe from 700,000 years ago (Parfitt, 2005).

Homo floriensis inhabited Indonesia at least for the period from 95-74 to 12 thousand years ago. Heights of two individuals have been estimated at 1.06 and 1.09 meters. The structure of the brain is most similar to Homo erectus but the size of brain relative to the body is comparable to australopithecines and chimps. It lacked a chin. While facial and dental features justify its classification in the genus Homo, it may not be a species of Homo erectus that evolved a shorter stature (Morwood, 2005). Flores humans had a brain the size of a grapefruit,
more similar in size to extinct hominids and modern apes than to ours.Despite this small size, Flores humans apparently used both tools
and fire (Associated Press, 2004).

Although Flores humans possessed brains comparable in size to those of chimpanzees, they apparently made use of advanced stone tools. Brain endocasts indicate that their frontal lobes were large and highly folded and that their temporal lobes were enlarged as well (Small but Smart?, 2005).The overall brain size (440 cubic centimeters) and the brain size/body size ration of Homo floriensis is similar to that of australopithecines. The shape of its brain, however, is more advanced and bears similarities to that of Homo erectus, although it is not simply a smaller version of a Homo erectus brain. Enlarged frontal lobes (Brodmann region 10) and temporal lobes, indications of the use of fire, stone tools, apparent predation on large mammals, and the fact that these hominids somehow traveled to the Indonesian island of Flores all indicate advanced intelligence (Falk, 2005). The oldest Homo floriensis fossils date from 38,000 years ago and the youngest from 18,000 years ago. It is presumed that they reached Indonesia by boat (Morwood, 2004). Brain analyses support the classification of Homo floresiensis as a separate species rather than a microcephalic modern human (Falk, 2007).

ARCHAIC Homo sapiens/ Homo heidelbergensis

DATES: 500 thousand
years ago to 200 thousand years ago

CHARACTERISTICS:

The earliest specimens classified as archaic
Homo sapiens or Homo heidelbergensishave features of both H. erectus and H. sapiens sapiens with robust skeletons and teeth.Some specimens have brow ridges, receding foreheads,
and receding chins.Some specimens
already display some neanderthal facial characteristics
(morphology of the eye sockets, cheekbones, and nasal bones) suggesting
that neanderthals may have diverged from other lineages quite early.There is an advanced expansion of the cranial vault and the average
cranial capacity was 1200 cc (Brauer, 1993; Howell, 1952; Trinkaus,
1997; Stringer, 1988; Stringer 1993; Arsuaga,
1997).

One significant change that occurred between
the archaic and modern humans was a shortening of the sphenoid bone in
the braincase.Externally, this
change resulted in jaws, which did not protrude to the same degree.Internally, the change could have had a much
more profound effect: it would have affected the dimensions of the oropharynx
and the variety of sounds that humans could have made in speech.(Chimps and gorillas are capable of large vocabularies
when using sign language and their use of signs suggests a degree of complex
thought which they were previously thought to be incapable of.Apes do not speak because they do not have the
anatomy for it.Thus changes in
the vocal tract could have had a much larger impact on language than increases
in brain size.) (Hublin, 1996;
Rightmire, 1997; Rightmire, 1976;
Holden, 1998).

The development of human speech required a movement of the splanchnocranium under the neurocranium, a movement of the tonge posteriorly, and the development of a pharynx which was longer and narrower (Davidson, 2005).

THE PIT OF BONES: In
Spain, the largest collection of Middle Pleistocene bones (1,600
bones from 32-50 individuals) was found dating at 300,000 years ago.Humans had been in Spain long before that: fossils of early Homo are known from 800,000
years ago and one site which has tools may be 1.2 million years old.As sea level rose and fell in the Pleistocene, there were times when
the water levels separating Morocco and Spain were only half the current level so this migration would not
have been difficult.Some feel that
the primitive characteristics of these skeletons (such as a brow ridge and
multiple roots for the premolars) warrant their classification as Homo antecessor, distinct from Homo heidelbergensis.If H.
antecessor is distinct from H.
heidelbergensis, it cannot yet be concluded whether H. heidelbergensis evolved from H.
antecessor or from African Homo,
(which bear similarities to H. heidelbergensis)
which arrived at central Europe through the Middle
East (Balter,
2001; Carbonell; 1995; Bermudez, 1997; Bahn, 1996).The lower jaw of Homo antecessor is intermediate between Homo sapiens and more primitive species of Homo (Carbonell, 2005).

Homo antecessor displays a mosaic of traits, such as primitive dental features and advanced aspects of the midfacial region, which indicate that it could represent the common ancestor of Neanderthals and modern humans (De Castro, 1997). Some have suggested that Homo erectus was not directly ancestral to modern humans and hominids such as Homo antecessor represent the common ancestor of Neanderthals and modern humans (De Castro, 1997). Homo antecessor possessed a styloid process (De Castro, 1997).

Homo neanderthalis

DATES: 230 to 30 thousand
years ago

SITES: throughout Europe east to Israel and Uzbekistan

CHARACTERISTICS:

Although some neanderthal
characteristics are found in modern humans or earlier Homo species, the combination of these characteristics in neanderthals
is unique.These characteristics
increased in frequency as later neanderthals evolved.As a result, there are differences between the robust “classic”
neanderthals of Western
Europe and the populations
of the Middle East.

Neanderthals had a long trunk, short legs, and
a robust skeleton.The size of muscle attachment sites imply considerable muscle power.A diastema (gap) exists between the jaw and lower wisdom teeth.The skull and face were long, the forehead low, there were protruding
brow ridges, the rear of the braincase was round (not pentagonal as in
modern humans), there was a large nasal cavity, the floor of the eye socket
was flat or even receding laterally, there was a strong mandible lacking
a chin, a protruding midface, the cheekbones were weak and oriented obliquely,
the occipital bone bulges posteriorly (the occipital bun, a trait which
very rarely can still occur in modern humans), and the occipital bone
has a conspicuous depression known as the sura-iniac fossa.Hand bones indicate that Neanderthals may not have been as dextrous as modern humans (Musgrave, 1971; Trinkhaus, 1982).Although neanderthal faces seem abnormally long, they are actually
similar to earlier specimens of Homo.Modern human faces are much shorter, including
the region of the pharynx which affects the ability to produce the sounds
of human speech (Trinkhaus, 2003).

Males averaged 5’6” in height but because
of their robustness, they may have averaged 30% larger than modern humans.The average brain capacity was 1450 cc (a little
larger than that of moderns) and one young male specimen had a capacity
of 1750 cc (Kappelman, 1997).While some concluded that neanderthal
nasal specializations make them unique among hominids, others have refuted
this (Schwartz, 1996; Laitman, 1996; Franciscus,
1999)..Some
neanderthal hand characteristics
are unique.Neanderthal hip morphology
suggests that they were more active as children.Some analyze this as a potential culture difference
between neanderthals and the modern humans that
replaced them (how active/mobile the young members of a group were).

Between 300 and 127 thousand years ago there
were two periods of glacial advance separated by a cool interglacial period
and many features of the Neanderthal body are adaptations to cold temperatures.Neanderthals have provided the first evidence of burying the dead
100 thousand years ago and later burials include animal bones and flint.One 47,600-year-old cave has an impressive 4-meter x 5-meter structure
built of stalagtites and stalagmites. Neanderthals arrived in Israel after modern humans and the two groups coexisted (with apparently
no exchange of technologies) for 60 thousand years (Bar-Yosef, 1993; Hovers, 1996).Neanderthals used fire and used more tools and weapons than Homo erectus.The types of tools used change very gradually
and the style of neanderthal tools are referred
to as Mousterian.At some sites,
human and ungulate bones are smashed to similar degrees, suggesting cannibalism
(Defleur, 1999; Jelinek,
1982). Neanderthal populations decreased at about the same time the European climate was becoming colder and drier about 35 to 40 thousand years ago (Mellars, 2006).

.In Southern
Spain, Neanderthals survive
5-10,000 years after modern Homo
sapiens appear in the north of Spain but they don’t acquire any new technologies.In other parts of Europe, Neanderthals do acquire new technologies just before their
disappearance, possibly as a result of interaction with modern Homo sapiens (Balter,
1996;).

The craniofacial differences between
Neanderthals and modern Europeans are greater than those observed between
the two species of chimpanzee and between all modern human populations.This suggests that Neanderthals were a separate
species (Harvati, 2003;Harvati, 2004).Genetic evidence
also supports this conclusion.Mitochondrial DNA was successfully isolated from neanderthal bone and the sequence was unlike any living human.Its variation from modern humans is roughly half of the difference
between humans and chimps. A second lab repeated this with identical results.
Analysis of Cro-Magnon DNA of about the same age identified a sequence which
was well within the variations of modern humans.The conclusion drawn from this genetic evidence is that neanderthals
are not related to living humans. An analysis of a fossil modern human mitochondrial
genome indicated that it also went extinct-- if this one human’s mitochondrial
genes are absent today, it is possible that neanderthals
interbred with modern humans and their mitochondrial lineages disappeared
as well.Although mitochondrial DNA from several Neanderthals
has identified DNA sequences which predate the origin of the mitochondrial
strains which are known in modern living humans, anatomically modern humans
from about 60 thousand years ago possessed a DNA segment on their mitochondrial
chromosomes which now exists in the nucleus of modern human populations.
Some feel that neanderthals
and modern humans did interbreed and that neanderthals
helped to contribute to European lineages (Caramelli, 2003; Adcook, 2001; Ward,
1997; Kahn, 1997; Mellars, 1998).There is one fossil find of a young human from
Portugal which may have a mix of neanderthal
and modern human characteristics (Zilhoao, 2000).

MODERN
HUMANS

The oldest remains of Homo sapiens sapiens are known from Ethiopia and have been dated at 195,000 years old (Wilford, 2005). East Africa underwent severe drought during the period of 135 to 75 thousand years ago. Lake Malawi, for example, seems to have been reduced to 95% of its original extent. This may have been a factor in the migration of some humans out of Africa (Scholz, 2007).Modern humans became
lighter and more gracile. (Gibbons, 1997).The sphenoid bone shortened, meaning that the
face did not project quite as far.The
skull became higher and rounder in contrast to the low, long skulls of
Homo erectus and Neanderthals (Lieberman,
1998).How did modern humans evolve?There are two different models.

--Replacement Model:

In the replacement model, it is thought that
somewhere between 1 million and 100,000 years ago, modern humans left
Africa, migrated throughout the continents, and completely replaced all
other hominids (such as Homo erectus,
Homo neanderthalis) so that they alone were ancestral to all modern
human groups.Proponents of this
model vary on the timing, often due to discipline; paleontologists favor
older dates, geneticists favor younger dates.One strong piece of evidence that is frequently
observed is that the greatest genetic difference in
human populations occur between African populations.The evidence for some of the oldest branches
of humanity exist in Africasuggest that humanity evolved in
Africa (Zischler, 1995; Waddle, 1994; Vigilant,
1991; Wood, 1997). Advanced tools (referred to as Acheulan; they included
items such as hand axes) first appear in Africa and are known outside Africa as of 500,000 years ago (Lewin,
1987).

--Regional Continuity
Model:

Although modern humans did leave Africa over 100,000 years ago, they interbred with the hominid populations
which were already present on other continents (Homo erectus in Asia, Homo neanderthalis in Europe) to produce many of the regional differences in modern humans.The discovery of apparently ancient DNA sequences in Asian and
Australian populations which are not found anywhere else in the world
supports the model of regional continuity (Harding, 1997; Holden 2001).Some anthropologists conclude that a number of fossil finds of
Homo erectus and Homo
neanderthalis have physical traits which
correspond to the modern humans from those regions from much later dates
(Wolpoff, 1993; Thorne, 1992; Thorne, 1981)
.

A Homo erectus skull from India supports a relationship to modern Homo sapiens in India (Sonakia, 2006). Asian fossils combine features of early modern humans with those of archaic human lineages, in support of the regional continuity model (Shang, 2007).European fossils which combine the features of modern humans and Neanderthals support the regional continuity model (Trinkhaus, 2007).

In comparing the microsatellite
DNA in the human genome, the most divergent patterns are observed in some
African populations, suggesting an African origin of humanity (Goldstein,
1995).Comparisons can be made between mitochondrial genomes (which
are primarily passed from women to their children) and Y-chromosome sequences
(which are passed from men to their sons).These comparisons tentatively
indicate that women have actually been more mobile than men (in that they
did not necessarily stay in the areas in which they were raised) and thus
were greater agents of gene dispersal (Pennisi,
2001).

The gene microcephalin (MCPH1) and its surrounding genes can exist in various forms, known as haplotypes. One form, known as haplotype D, is found in 70% modern humans. Although the haplotype seems to have spread through human populations several tens of thousands of years ago, the degree of nucleotide divergence between members of the same haplotype is far greater than what would be expected. One explanation is that interbreeding between archaic humans and modern Homo sapiens resulted in a beneficial set of alleles which were then positively selected for (Evans, 2006).

Modern humans arrived in Australia by 40-60,000 years ago (there are sites in East Timor which are slightly younger at 35,000 years old).The Clovis culture of big game hunters is known in the New World as of 12,000 years ago.In
recent years, there have been a number of pre-Clovis
sites found in both North
America (ranging from
12-19,000 years old) and even in Chile (12,500 years old).The
ancestry of the first Americans may be more complex than what was first
thought—some skeletal traits of fossils and genetic analyses indicate
that native Americans are more similar to Europeans
than Asians (Marshall, 2001; Pena, 1999; Gibbons, 2001; Holden, 1996;
Morell, 1998).

Molecular analyses point to three groups
of aboriginal Americans: Amer-Ind, Na-Dene,
and Eskimo.The Na-Dene and Eskimo
might not represent separate migrations but rather early offshoots of
the Amer-Ind group which were isolated in northern regions by
changing climates (Bonatto, 1997).